Froth generator



1965 J. c. RILL, JR, ETAL 3,220,801

FROTH GENERATQR Filed May 31, 1962 3 Sheets-Sheet 1 INVENTORS' Nov. 30,1965 J. c. RlLL, JR., ETAL 3,220,801

FROTH GENERATOR Filed May 31, 1962 3 Sheets-Sheet 2 7 M7 M1 9 INVENTORS'John 61 R12), J2:

Paul (ff/1426f??? Nov. 30, 1965 J. c. RILL, JR, ETA]. 3,22,80l

FROTH GENERATOR Filed May 31, 1962 5 Sheets-Sheet 5 Fneau SUPPLY TIM uvVENTORS John C: fli/Z, Jr. Pea} E S/zaeffer United States Patent ()flicePatented Nov. 30, 1965 3,220,801 FROTH GENERATOR John C. Rill, Jr.,Dayton, and Paul F. Shaelfer, Lewisburg, Ohio, assignors to GeneralMotors Corporation, Detroit, Mich., a corporation of Delaware Filed May31, 1962, Ser. No. 199,095 3 Claims. (Cl. 23252) This invention pertainsto chemistry and more particularly to mixing apparatus and mixingprocesses for making polyurethane foam-forming materials in an expandedform known as froth.

Cellular polyurethanes were first formed from a liquid mixture ofcomponents. Strong molds have been required to prevent the bulging ofthe walls when such liquid mixtures are poured into the molds because ofthe pressure which develops during the change in phase and thermalexpansion of the gas in the mold, resulting in a volume increase of over3600%. The expense and difficulties of providing such strong molds andreinforcing fixtures has been a strong deterrent to the extensive use ofthe polyurethane foams. Recently a new process producing polyurethanefroth has been developed in which the fluorocarbon expansion agents inthe polyurethane change from the liquid to the gas phase and areexpanded before depositing in the place where it is to be lodged.

Although the froth is capable of expanding several times, the pressuresgenerated are relatively small and no thick-walled molds or reinforcingfixtures are required. In many instances the froth can be depositeddirectly in the insulation space in the final products without the useof reinforcing fixtures for the walls thereof. However, one difficultyis to obtain low density, high uniformity and high insulating value withthe froth-type foam. Another difficulty is that the froth tears readilyand often has the membranes and cell walls ruptured permitting leakageof insulation gas from the cells and coagulation of the gas bubblesproducing heterogeneously dispersed large cells which severely limit theattaining of low coefficient of thermal conductivity in the foam.

It is an object of this invention to provide a froth generator in whicha froth of high quality and uniformity with low density and highinsulating value can be produced whenever and for as long as desired.

It is another object to provide a froth generator which will deliver thefroth by streamline or laminar flow.

It is another object of this invention to provide a froth generator inwhich substantially constant pressure is maintained in the mixingchamber at all times.

It is another object to produce a froth generator capable of producing afroth mixture that expands from the heat of final polymerization lessthan greater than the froth density.

These and other objects are attained using the apparatus and the processshown in the drawings in which the two polyurethane components such asthe component containing the hydroxyl bearing polyol surfactant andcatalyst hereinafter referred to as master batch and the isocyanatebearing component are circulated in separate systems and metered into anenclosed mixing chamber in stoichiometric ratio. A volatile liquid isalso discharged separately into the mixing chamber in proportion to thedelivery of the two aforementioned components. An agitator is rotated athigh speed within the mixing chamber. The bearings for the agitator aremaintained lubricated by lubricant under high pressure which may beprovided with a cooling system. The outlet of the mixing chamber isprovided with a loaded pressure relief valve for maintaining apredetermined relatively high constant uniform pressure within themixing chamber. The outlet or diffuser of this loaded relief valve isflared at a proper angle which provides streamline or laminar flowproportioned to the Reynolds number of the components and the rate ofexpansion of the froth as the pressure drops from expansion chamber toatmosphere. The delivery of the components may be controlled by a timingdevice which, in addition, may provide for automatic flushing of themixing chamber and the pressure relief valve following each usage of thefroth.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawings wherein a preferred embodiment of the present invention isclearly shown.

In the drawings:

FIGURE 1 is a vertical sectional view of the froth generator embodyingone form of my invention;

FIGURE 2 is an irregular sectional view taken along the lines 22 ofFIGURE 1;

FIGURE 3 is a fragmentary view of the mixing head in section showing thevalves positioned for flushing; and

FIGURE 4 is a diagrammatic view of the froth generating system.

Referring now to the drawings and more particularly to FIGURES l to 3,there is shown a froth generator 20 provided with a valve block 22containing two parallel plug valves 137 and 139 each having twotransverse parallel passages designated respectively 141, 143, and 147located in the same plane perpendicular to the axis. When the valves 137and 139 are turned to the delivery position, the passage 141 becomessubstantially aligned with the polyisocyanate inlet fitting 149 and thedelivery passage 151 which delivers into the mixing chamber 157.Similarly, the passage 145 becomes substantially aligned with theactivator inlet fitting 153 and its passage and the delivery passage 155which delivers into the mixing chamber 157. These valves 137 and 139 arepreferably made of 7% glass fiber reinforced, polyethylene orpolytetrafluoroethylene or polypropylene. As shown in FIGURE 2 thevalves 137 and 139 are pressed respectively into the tapered recesses159 and 161 by the compression-type coil springs 163 and 165 which areheld in place by the threaded plugs 167 and 169. At their opposite endsthe valves 139 have the cylindrical shafts 171 and 173 extending throughthe plasitc bearings 175 and 177 Within the valve block 22.

The outer ends of the shafts 171 and 173 are provided with squarereduced end portions 179 and 181 on which are slidably mounted thepin-type clutches 183 and 185. These pin-type clutches 183 and 185normally have their pins 187 urged into the apertures in theintermeshing gears 189 and 191 by the coil springs 1937 With theclutches 183 and 185 engaged the valves 137 and 139 will be rotatedsimultaneously by the toothed rack 195 which engages the teeth of thegear 189 to rotate both gears 189 and 191 and the valves 137 and 139simultaneously. The rack 195 is operated by the double-acting aircylinder 197 which has its opposite ends connected by the deliveryconduits 199 and 220 to the four-way valve 222 which is operated by thesolenoids 224 and 226 10- cated at the opposite end thereof. The air issupplied from a compressor (not shown) through the supply conduit 228 toa regulating valve 230 which controls the flow of air into one branch ofthe air control system so as to maintain the pressure within this branchof the air system at approximately 125 pounds per square inch. Thisbranch of the air control system includes a branch conduit 232connecting with the central portion of the three-way valve 222 which isprovided with discharge connections at the opposite ends connecting withthe discharge conduits 234 and 236. The solenoids 224 and 226 areconnected by the conductors 238 and 240 with a timer 42 which controlsthe supply of electric energy to the conductors 238 and 240 so as tohold the valves 137 and 139 open for a definite period of time and thenrecloses these valves. The timer 242 is connected by the switch 244 tothe supply conductors 246.

At the rear of the mixing chamber 157 is a passage 248 connecting withthe discharge outlet of an injector nozzle 250 of the pintle type. Thisinjector nozzle may be of the same type used for injecting of fuel intothe cylinders of a diesel engine, if desired. It is made to operate onpressures of about 300 to 350 pounds per square inch sufficient to keepthe injecting expansion agent in the feed line in the liquid phase. Thisnozzle may be of the type shown in Marks Mechanical Engineers Handbook,Fourth Edition, Tenth Printing, April 1947, as shown in FIGURE 52b onpage 1298 thereof, or it may, for example, include an injection nozzleholder No. KCA30SD2 with the nozzle DN4S2 made by the Robert Bosch,G.m.b.H. of Stuttgart, Germany. A volatile liquid, such asdifluorodichloromethane, is stored in the supply tank 252 from which thevolatile liquid is delivered by the variable delivery pump 254 driven bythe motor 256 through the conduit 258, the solenoid valve 260 and theconduit 262 to the injector nozzle 250. The solenoid of the valve 260 isconnected by the conductors 265 to the timer 242 in such a way that thevalve 260 will be open whenever the air cylinder 197 is in the positionto deliver the polyurethane components to the mixing chamber 157. Thepump 254 is adjusted so as to supply the volatile liquid to the injectornozzle 250 at a pressure of between 300 and 350 pounds so that a widelydistributed spray issues from the nozzle 250 into the mixing chamber157.

The mixing chamber 157 is provided with a projecting pin-type agitatorfor thoroughly mixing the components of the polyurethane with thevolatile liquid until the liquid completely penetrates the twocomponents. The agitator 264 is fastened to the lower end of theagitator shaft 266 driven at its upper end above the valve body 22 by anelectric motor 268. The shaft 266 is surrounded by a hardened ring 270sealed within a recess in the valve body 22 by an O-ring seal. Also,sealed to the valve body 22 is a bearing housing 272 provided with alower needle bearing 274 and an upper ball bearing 276. The bearinghousing 272 is also provided with a recess receiving the hardened ring278 sealed with an O-ring seal to the housing 272. Between the rings 270and 278 the bearing housing 272 is provided with a shaft seal chamber280 containing an upper running seal 282 bearing against the lower faceof the ring 278 and a lower running seal 284 bearing against the upperface of the ring 270. Between these rings 282 and 284 is acompression-type coil spring 286 supplying the force to hold the rings282 and 284 against the adjacent faces of the rings 278 and 27 0. Therings 288 and 290 of elastomeric material are provided for sealing therunning seal rings 282 and 284 to the shaft 266. The shaft seals 282 and284 are lubricated by a lubricating system including a pump 292 whichdischarges the chemically inert lubricant into the shaft seal chamber280. The lubricant is recirculated through the outlet 294 and thecooling conduit 296 back to the inlet of the pump 292. A relatively highpressure such as about 200 pounds per square inch is maintained in theseal chamber 280 for preventing any of the components of the mixturefrom flowing upwardly out of the mixing chamber 157 around the shaft266. This lubricant pressure also assures good lubrication for therunning shaft seals 282 and 284.

The prepolymer or isocyanate bearing component is delivered from thesupply tank 321 through a conduit 323 to the variable delivery pump 325driven by the electric motor 327. The pump 325 is adjusted to deliverthe prepolymer or isocyanate bearing component through the conduit 329to the inlet 149 at a rate calculated to give the desired ratio of thiscomponent to the other components supplied to the mixing chamber 157.When the plug valves are in the recirculating position shown in FIGURE3, the resin is returned through the outlet 331 and the return conduit333 to the tank 321. The tank 321 includes a mixer or agitator 335driven by the electric motor 337. It also includes a jacket 339preferably of insulating material and air space which may contain anelectric heater 341 controlled by the thermostatic switch 343 responsiveto the temperature of the thermostat bulb 345 located within theinsulated enclosure 339. The conduits 329 and 333 are surrounded by theelectric heaters 347 and 349 which are either manually orthermostatically controlled in response to the temperature of the valveblock 22.

The activator component is supplied from the supply tank 351 through theoutlet conduit 353, the variable delivery pump 355 driven by the motor357 and the feed conduit 359 to the activator inlet 153. When the valvesare turned to the recirculating position shown in FIG- URE 3, theactivator component passes from the inlet 153 through the passage 147 inthe valve 139 to the recirculating outlet 361 which connects through thereturn conduit 363 with the tank 351. The contents of the tank 351 areagitated by the agitator 36S driven by the electric motor 367. The tank351 is enclosed within an insulating jacket 369. The space between thejacket 369 and the tank 351 may be heated by an electric heater 371under the control of the thermostat 373 having a thermostat bulb 375within the jacket 369.

The conduit 359 may be surrounded by the electric heater 377 while thereturn conduit 363 may be surrounded by the electric heater 379. Each ofthese heaters may either be manually controlled or controlled accordingto the temperature of the valve block 22. If it is desired to operatethe tanks 321 and 351 at temperatures below room temperature at anytime, they may be surrounded by the refrigerant evaporators 381 and 383which have their outlet connected through the evaporator regulatingvalves 385 and 387 and the suction conduit 389 to the inlet of thecompressor 391 which is driven by an electric motor 393. The compressor391 delivers the compressed refrigerant to the condenser 395 from whichthe liquid refrigerant is delivered through the supply conduit 397 underthe control of the regulating valves 399 and 420 to the thermostaticexpansion valves 422 and 424 having their thermostat bulbs in contactwith the outlet of the evaporators 381 and 383. These expansion valves422 and 424 deliver the liquid refrigerant under reduced pressure to theevaporators 381 and 383 where the liquid refrigerant evaporates to coolthe tanks 321 and 351.

The mixing chamber 157 is enclosed in a mixer housing 426 provided withan outlet connection 428 of ample size to provide for streamline orlaminar flow of the reactants from the chamber 157. This outletconnection 428 is connected to an annular pressure relief value 430 ofsuch design and capacity as to provide for streamline or laminar flow ofthe reactant mixture. This pressure relief valve is provided with aninlet chamber 432 Within a cap member having at the bottom a passageblocking wall and radial passages 434 above said wall extendingoutwardly from the chamber 432 into the space 438 enclosed by the sleeve436 of elastomeric material which is sealed at both ends. This space 438surrounds the inlet portion of the pressure relief valve 430 as well asthe outlet portion 440 containing the discharge passage 442. Between theclosed or plugged end of the inlet fitting or cap member containing thechamber 432 and the open end of the outlet fitting 440 is a gap 439through which the mixture flows after emerging from the passages 434 andflowing downwardly around the closed end of the inlet fitting. An airchamber housing 444 surrounds the sleeve 436 and is connected by thefitting 446 and the conduit 448 with the three-way solenoid operatedvalve 450. This valve 450 is supplied through the conduit 452 from themanually adjustable pressure regulating valve 453. The operatingsoleniod of this valve 450 is connected by the conductors 456 to thetimer 242 so that during the delivery period it connects with thebranched supply conduit 452 and during the recirculating period it isconnected to the exhaust conduit 454. The valve 453 is adjusted todeliver air at a pressure of between 70 and 100 pounds per square inchin accordance with the total flow rate and the volatile liquidconcentration to obtain the best product.

To illustrate typical operation, the application of 70 to 100 pounds ofair pressure surrounding the sleeve 436 contracts the sleeve into thespaces 438 and 439 and by cooperation of the sleeve 436 with theadjacent outer surface of the bottom wall of the inlet chamber 432maintains a pressure within the mixing chamber 157 at about 90 to 125pounds per square inch. The maintenance of a substantially uniform highpressure within the mixing chamber 157 assures high quality cell latticeuniformity consistent with low density of the cellular polyurethane. Thevolatile liquid is uniformly distributed throughout the mixture. Theoutlet fitting 440 is provided with a flared discharge nozzle ordiffuser 458 which diverges at a rate to provide streamline or laminarflow proportional to the Reynolds number of the components and the rateof expansion of the froth as the pressure drops from the expansionchamber to atmosphere. For example, for a flow rate of 200 feet perminute, the nozzle preferably has a diameter of 1% inches at the top and1% inches at the bottom. The included angle of the flare is about Theflared portion has a length of about 2%; inches. It expands the mixturefrom 100 pounds per square inch gage and a density of 72 pounds percubic foot down to atmospheric pressure and a density of about 2.5pounds per cubic foot. The lower rim is chamfered externally at an angleof about 30 to the axis as indicated by the reference character 460 soas to provide a sharp edge at the bottom of the flared section toprevent any material from curling upwardly or otherwise adhering at thispoint. The mixture issues from the flared outlet 458 with a consistencyresembling aerated shaving cream. After it is deposited in theinsulation space or other place wherein it is to be located, theexothermic reaction of the ingredients raises its temperature so that itexpands about thereby reducing its density to between 1.7 and 1.8 poundsper cubic foot. This material, when the reaction is completed and thematerial is cured, provides a strong product which will retain its highinsulating value for many years.

As one specific example, the tank 321 may be charged with 100 partsprepolymer F. The prepolymer F is composed of 75 parts of polyisocyanateingredient A and parts of polyether C. The isocyanate ingredient A iscomposed of 80 parts 2,4 diisocyanate and 20 parts of 2,6 diisocyanate.The polyether C contains 1 mol of sorbitol and 10 mols of propyleneoxide. It has an OH number of 495, an acid number of .30 and a viscosity(cps.) at 83 F. of 7500. The water by weight is less than .05%. The tank351 is supplied with a mixture of parts of polyether C to 29.5 parts ofactivator mixture 1. The activator mixture I, expressed in parts byweight, includes 26 parts of N,N,N',N'-tetrakis (Z-hydroxypropyl)ethylene diamine, 3 parts triethylene diamine,

6 and .5 part emulsifier made up of propylene glycol and 10%polyethylene glycol. The tank 321 is kept at a temperature of betweenabout 80 and 82" F. while the tank 351 is kept at a temperature betweenabout 98 and 102 F. The ingredients in the proportion of partsprepolymer F from the tank 321, 59.5 parts activator I from the tank 351and 20 parts difluorodichloromethane from the tank 252 are mixed in themixing chamber 157 to form the froth. The froth leaves the nozzle at atemperature of between about 80 and 85 F.

The apparatus includes provision for automatically flushing the mixingchamber 157, the agitator 264, the outlet 428 and the passages 432, 434,438 and 442 after each delivery. For this purpose a suitable solventsuch as trichloroethylene or methylene chloride is delivered through thepipe 462 to the solenoid valve 464 which is electrically connected bythe conductors 466 to the timer 242 to open the valve 464 for a briefperiod such as five seconds following the termination of each delivery.This valve 464 supplies the solvent through a pipe 468 through the inletconnection 470 in the valve body 22. When the valves are in the positionshown in FIGURE 3, this solvent is delivered through the passage 472which delivers the flushing liquid through the passage and the branchpassage 474 into the passage 157 which leads into the mixing chamber157. This flushing liquid flushes out the components out of the mixingchamber and the passages connecting therewith so that they will notcongeal. After the five second solvent flushing, the timer 242 closesthe valve 464 and through the conductors 480 opens for ten seconds theair solenoid valve 482 to allow air from the branch conduit 484 to flowinto the conduit 468 which supplies the air to the flush inletconnection 470, the passages 472, 145, 174, to the mixing chamber 157,the pressure relief valve 430 and the discharge nozzle 458. This removesthe solvent from the apparatus. The mixture flushed out is delivered toa waste drum.

While the embodiment of the present invention as herein disclosedconstitutes a preferred form, it is to be understood that other formsmight be adopted.

What is claimed is as follows:

1. A froth generator including an enclosure enclosing a mixing chamberprovided with an outlet, means for delivering components to the mixingchamber, said mixing chamber being provided with a cap-shaped outletmember having laterally extending outlet passages, an outlet nozzlespaced from said cap member having an endless entrance rim adjacent saidcap member spaced at a substantially uniform distance away from the capmember throughout its adjacent surface, a flexible sleeve surroundingthe outlets in said cap member and the space between said rim and saidcap member, means for sealing the ends of the sleeve to the cap memberand the nozzle, means providing a sealed enclosure surrounding saidsleeve, and means for applying a fluid under pressure to said sealedenclosure.

2. A polyurethane froth generator including an enclosure enclosing amixing chamber, means for delivering predetermined proportionedquantities of polyurethane forming components to the mixing chamberincluding a volatile liquid gas generating ingredient, mixing means insaid mixing chamber for mixing said components, valve means forcontrolling the discharge of said components into said mixing chamber,said mixing chamber being provided with an outlet passage having in it acoaxially aligned circular passage blocking means, an outlet nozzlespaced from said passage blocking means having a circular entranceadjacent to and spaced at a substantially uniform distance away from andcoaxially aligned with said passage blocking means throughout itsadjacent surface, a flexible sleeve surrounding and concentric with saidpassage blocking means and having one end sealed to the full peripheralextent of said nozzle, means for sealing the other end of said sleeve tosaid mixing chamber enclosure peripherally around said outlet passage,and means for substantially uniformly concentrically contracting saidflexible sleeve around said passage blocking means to control the flowof fluid from said mixing chamber substantially uniformly around saidpassage blocking means to said nozzle.

3. A generator as specified in claim 2 having means providing a sealedenclosure surrounding and sealed to end portions of the flexible sleeve,and means for applying a fluid under pressure to said sealed enclosurefor contracting the sleeve, said outlet nozzle having a flared dischargepassage which diverges at a rate to provide laminar flow of the fluid.

References Cited by the Examiner UNITED STATES PATENTS Hoffman 27762 Arf27762 Hoppe et al.

Corby et al.

Hampshire.

Geldern et al. 23252 Cole 23-252 MORRIS O. WOLK, Primary Examiner.

JAMES H. TAYMAN, JR., Examiner.

2. A POLYURETHANE FROTH GENERATOR INCLUDING AN ENCLOSURE ENCLOSING AMIXING CHAMBER, MEANS FOR DELIVERING PREDETERMINED PROPORTIONEDQUANTITIES OF POLYURETHANE FORMING COMPONENETS TO THE MIXING CHAMBERINCLUDING A VOLATILE LIQUID GAS GENERATING INGREDIENT, MIXING MEANS INSAID MIXING CHAMBER FOR MIXING SAID COMPONENTS, VALVE MEANS FORCONTROLLING THE DISCHARGE OF SAID COMPONENTS INTO SAID MIXING CHAMBER,SAID MIXING CHAMBER BEING PROVIDED WITH AN OUTLET PASSAGE HAVING IN IT ACOAXIALLY ALIGNED CIRCULAR PASSAGE BLOCKING MEANS, AN OUTLET NOZZLESPACED FROM SAID PASSAGE BLOCKING MEANS HAVING A CIRCULAR ENTRANCEADJACENT TO AND SPACE AT A SUBSTANTIALLY UNIFORM DISTANCE AWAY FROM ANDCOAXIALLY ALIGNED WITH SAID PASSAGE BLOCKING MEANS THROUGHOUT ITSADJACENT SURFACE, A FLEXIBLE SLEEVE SURROUNDING AND CONCENTRIC WITH SAIDPASSAGE BLOCKING MEANS AND HAVING ONE END SEALED TO THE FULL PERIPHERALEXTENT OF SAID NOZZLE, MEANS FOR SEALING THE OTHER END OF SAID SLEEVE TOSAID MIXING CHAMBER ENCLOSURE PERIPHERALLY AROUND SAID OUTLET PASSAGE,AND MEANS FORSUBSTANTIALLY UNIFORMLY CONCEN-